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|Description Text||We use a concrete tapered end section for speeds 40 mph or less on permanent and temporary. We show on our drawings a 5:1/6:1 type transitions vertically. I can’t find the history on this and thought you might have some history on the tapered end section. I know the RDG indicates 20’ minimum length down to 4” from probably 32”. This is around an 8:1 transition.
I appreciate your help!
|Date||February 20, 2014|
|Response||You are correct that the RDG does allow this on lower speed facilities when space is limited. However, this vertical taper has never been crash tested successfully to my knowledge.
Vertical tapers have been tested at TL-2 for low profile PCB designs at TTI. However, these were at TL-2 speeds and had barrier heights of 20” or less, not the 32” specified here.
The taper guidance in the RDG is likely based on information in NCHRP Report 358. Previous computer simulations of the sloped end treatment, as shown in NCHRP Report 358, found that the sloped end treatment for a 32" high barrier can cause overturn of the vehicle for impact speeds of 30 mph or greater.
We have answered a similar question for MoDOT in the past. See the response below as it details the testing of sloped end treatments and our recommendations.
|Date||March 4, 2014|
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